For many years plastic deformation has been used to structurally alter and to enhance the physical properties of different materials. In particular, hot working is a universally accepted method for defect removal and achievement of high ductility and strength mechanical properties associated with cast ingots. Traditional metal forming processes such as forging, rolling and extrusion have also been used for defect removal and enhancement of mechanical properties of selected materials. These processes are often associated with multiple reductions of the original cross section of the selected materials. For example, to guarantee high quality products from aluminum-based alloys, the total reduction or the ratio of the original ingot cross section to the finished product cross section may be as high as 50 to 1. Traditional metal forming operations are also characterized by high stresses and large applied forces which frequently result in significant non-homogeneity of the work piece. As a result, it is often necessary to use powerful and complex machines, which are quite expensive, to produce a satisfactory finished product.
Traditional extrusion processes are frequently directed towards changing the initial shape or cross sectional area of the work piece to the desired shape for the finished product. Such extrusion processes have experienced significant limitations in producing large cross sections and bulk products as well as processing many advanced alloys and composite materials. The problems and limitations are particularly apparent, when the desired results are dependent upon the stress-strain history associated with the extrusion process. Traditional deformation processing equipment and methods are also frequently very expensive and experience high scrap rates related to non-uniformities which may develop in the work piece. Previously available deformation processing equipment will often not satisfactorily process products with large cross sections.
Die assemblies have previously been provided for deformation processing of selected materials by extrusion through two or more extrusion channels disposed at an angle relative to each other and having equal cross sectional areas. These previous die assemblies were often unsatisfactory for deformation processing of high strength, brittle materials due to excessive friction forces associated with movement of the material from one channel into a second channel. Temperature differences also often occurred between different portions of the die assemblies and the material being extruded. Attempts have been made to overcome these limitations by using expensive, complex machinery to apply hydrostatic back pressure to brittle and low ductility materials during the extrusion process. The costs associated with such deformation processing equipment and methods have been very high and the results have been less than satisfactory.